The present invention relates generally to air dryers, and more specifically, to an air dryer with an integral pre-filter for a brake system for vehicles.
Air dryers employing membranes consisting of a permeable membrane are capable of blocking the passage of nitrogen and oxygen molecules, but allowing water vapor molecules to pass through, as described in U.S. Pat. Nos. 6,719,825 and 5,525,143 amongst many others. In one variation of the technology, the air to be dried passes through the center of the membrane element. The membrane permits the passage of the water vapor to the outside of the membrane, but prevents the passage of the air to the outside of the membrane, thereby drying the air.
To work effectively, the outside of the membrane must be kept dry and at a lower pressure than the inside, creating the partial pressure differential to drive the water vapor out. This is done by providing some fraction of the dry output air as a counter flow sweep air across the outside of the membrane. The sweep air can be provided by sweep air orifice(s) connecting the dry air in the membrane air dryer outlet to the sweep air chamber surrounding the outside of the membrane. The orifices control the volume of sweep air, typically 10-20% of the dryer capacity and create a pressure drop in the sweep air volume. The sweep air and entrapped moisture are expelled to atmosphere.
U.S. Pat. No. 6,719,825 shows a control valve at the inlet for the sweep air. U.S. Pat. No. 5,375,620 shows a self-adjusting flow metering device for the sweep air. An air dryer including a coalescing and charcoal pre-filters and a membrane filter is also shown by U.S. Pat. No. 6,719,825.
The present disclosure is directed to a filter having a housing with at least a coalescing filter element, two drains in the housing and a drain valve assembly connected to the drains. The drain valve assembly includes first and second pneumatic valves each having an inlet connected to a respective drain, an outlet and a valve element for selectively connecting the inlet to the outlet in response to a pilot pressure on a pilot port. A third electric-pneumatic valve is connected to the pilot port of each first and second valves for providing the pilot pressure from an inlet port to the pilot ports when the third valve is actuated. The filter includes a heater positioned adjacent the first and second valves.
The disclosure is also directed to a filter having a check valve connected in parallel to the filter's inlet and outlet to bypass the filter when pressure at the inlet exceeds the pressure at the outlet by a set value.
The disclosure is also directed to a filter including a membrane separator mounted in a bore of the housing and extending cantileverly from the housing and the housing includes circumferentially spaced vanes extending along an axis of the bore. An end of the bore is a split collar and a clamp secures the membrane separator in the split collar. The bore has two axially spaced circumferential recess connecting the bore to a source of sweep air and an exhaust port respectively. A sweep air inlet and a outlet on a circumference of the membrane separator are aligned with respective recess and at least one of the recesses is in the reservoir.
The filter includes a conical filter element connected in series between the filter inlet and an inlet of the membrane separator and the filter element has a larger diameter at an inlet of the filter element than a diameter at an outlet of the filter element. An annular chamber connects the filter inlet to the filter element inlet and an end face of the filter element forms a wall of the annular chamber. The housing includes first and second portion removeably connected to each other; and the filter element includes a flange at the inlet of the filter element clamped by the first and second portions.
The filter is to be mounted in a reservoir inlet and extending into the interior of the reservoir so that an inlet of the filter is the inlet of the reservoir and an outlet of the filter is interior the reservoir. The drains are exterior the reservoir.
These and other aspects of the present method will become apparent from the following detailed description of the method, when considered in conjunction with accompanying drawings.